Purification of metals



Patented May 8, 1945 PURIFICA'rIo'N or METALS Peter P. Alexander, Marblehead, Mass., assignor to Metal Hydrides Incorporated, Beverly, Mass., a corporation of Massachusetts Application March 5, 1943, Serial No. 478,095

22 Claims.

This invention relates to the purification of metals contaminated with metal impurities having a. lower boiling point, and has for its object more particularly certain improvements in the method of purifying calcium, strontium and barium contaminated with sodium and potassium.

The alkaline earth metals, calcium, strontium and barium, are usually made by subjecting their fused chlorides to electrolysis. Since the salts of the alkali metals, sodium and potassium, are usually present in these chlorides, the resulting alkaline earth metal is usually contaminated with a small amount of alkali metal, as well as of the chloride of the alkaline earth metal itself. To purify the alkaline earth metal, it has been pro'- posed to subject the metal to distillation in a closed retort that has been evacuated to remove objectionable air. The distilled metal is permitte'd to condense in a cooler part of the retort, usually in the form of a more or less spongy deposit. After cooling the retort, air is admitted,

the retort is opened and the condensed metal is removed. 'I'he resulting product is so reactive that it frequently oxidizes rapidly on the surface and produces heat in sufficient amount to ignite the whole mass, with the result that res are quite common. This objectionable result is all dium and potassium, may be segregated from'the j 40 alkaline earth metals in a form to'make them non-inflammable on exposure to the oxidizing influence `of air. The alkaline earth metal may ythen be separately collected and at the sainev time be substantially freed of its chloride.

In accordance with the invention, the alkaline earth metal is heatedA in the absence of air to a temperature sulciently high-to distill the alkali metal impurity. The alkali metall vapor is selectively oxidized'by bringing it in reactive 'contact with a refractory oxide, such as titanium oxide, zirconium oxide and lchromium oxide, and col` lecting the oxidized alkali metal impurity as a solid separate from the alkaline earth nietal to -be purified. The alkaline earth metal itself is ad- Fig. 2 is a horizontal section on the line 2%-2 of Fig. 1.

The apparatus shown comprises an outer retort I0 supported Within a heating furnace II, the retort being held in position by means of two or more supports I2 restingr on top of the heating furnace. The retort preferably consists 'of heatresistant steel. It is provided with a removable cover I3 having attached thereto'a vertical pipe I4 and lateral valved branches I5 and I6, connectablewith a source of vacuum, and air, respectively. A removable inner retort 20, having an open top, rests within the outer retort. A removable tray 2l rests over the open top of the retort,

being supported thereon by means of three or more lugs 22 extending over the wall of the inner retort.v The heating furnace II consists essentially of a rectangular chamber 23 having a refractory bottom 24, side and end walls 25, and a -top 26 4having an opening of a size adapted to receive the 'outer retort. An expanding opening 2l is provided at or near a lower corner of one of the sidewalls of the chamber, for the introduction of heating gases into the chamber. A similar opening 28 is preferably provided at or nearl an opposite corner, as a spare or auxiliary means for introducing heating, or cooling, gases into the chamber. When not in use, the opening 28 is closed.l A flue opening 29 extends through the same wall as the opening 2l, preferably at a higher level, so that heating gases passed into the chamber through the opening 2l tend vto pass around lthe retort before leaving the chamber through the flue opening 29.

The apparatus may be used as follows: A charge of calcium, for example, contaminated with sodium, potassium, and calcium chloride, is placed in the bottom of the inner retort 20. V'I'he inner retort' is then placed in the outer retort I0. A layer of titanium oxide 30 is placed inthe tray 2|, which is in turn placed across the open top of the inner retort. The removable cover I3 is placed on the outer retort I0 and locked thereon .to provide a sealed joint. The lateral branch l5 is then connected to a source of vacuum. With the valve of this lateral branch open, and the valve of the other lateral branch I6 closed, the outer and inner retorts are placed .under vacuum to remove objectionable air.

Heating gases are passed through opening 21 into the heating chamber, where they circulate almost completely around the retort and then pass through the flue opening 29 to the outside atmosphere. Asthe lower portion of the outer retort I is heated, the lower portion of the inner retort is also heated. As the temperature rises, a point is reached where the sodium and potassium present in the calcium are distilled. The resulting sodium and potassium vapors rise to the upper and cooler portion of the retort where they .come in contact with the titanium oxide 3U inthe tray 2l. Due to their great afiinity for oxygen, the sodium and potassium arepromptly oxidized and the titanium dioxide is reduced to titanium and a sub-oxide of titanium, according to reactions vwhich may be indicated as follows:

retort continues to rise, a point is reached where the calcium is distilled and its resulting vapor l tends to condense and settle out against the wall of the inner retort immediately below the tray I6. Some calcium Vapor may of course rise sufciently to come in contact with titanium dioxide in the tray and react with it in a manner similar to sodium or potassium vapor. The bulk of the distilled calcium may, however, be separately condensed and collected, as shown. A residue consisting essentially of calcium chloride, admixed perhaps with a small amount of sodium chloride or potassium chloride, or both, remains as a residue in the bottom of the inner retort.

The introduction of heating gases to the heating chamber is stopped and the retort is permitted to cool. The cooling "operation maybe Vaccelerated by passing cooling air through the heating chamber, for example, through the opening 2B, or by removing the outer retort and its contents from the heating chamber. After the retort has been suitably cooled, lateral-branch I6 is opened to admit air to the interior of the retorts, after which the cover I3 is removed. The inner retort and tray are pulled'out of the outer retort; the tray is removed, and the condensed calcium is scraped off and separately recovered. The residues are advantageously removed by washing the inner retort with water.

It will be clear to those skilled in this art that the invention lends itself to numerous modications. Strontium and barium may be similarly treated to remove sodium and potassium, and to convert these explosive alkali metals into harmless compounds. Instead of titanium oxide, other suitable refractory metallic oxides, such as zirconium oxide and chromium oxide, may be employed, either separately or admixed.

In the practice of the invention, advantage is taken of the relative boiling points ofthe metals. The boiling points of sodium and potassium are substantially below those of calcium, strontium and barium. The temperature of the metal to be purified is therefore gradually elevated to a point where the metal impurity of lower boiling point is distilled. By heating its bottom, the retort is caused to yield a graduated temperature range. Since the sodium and potassium have the lower boiling points, their vapors tend selectively to rise highest in the retort. Since the calcium, strontium and barium have the higher boiling points, their vapors tend not to rise as high in the retort. They soon meet a. temperature environment conducive to condensation. In other Words, the alkaline earth metals may be made t0 condense inan intermediate section of the retort where the temperature is high enough to keep the alkali metals in vapor form. The alkali metal vapors, on the other hand, tend to rise to a cooler portion of the retort, where they were heretofore condensed, but where they are now converted into harmless compounds in accordance with the present invention.

I claim:

l. In the method of purifying calcium contaminated with a metal impurity of lower boiling point, the improvement which comprises heating the calcium to a temperature at which the metal impurity of lower boiling point but not the calcium is distilled, selectively oxidizing the resulting metal impurity vapor in a zone' removed from the main body of calcium, and collecting the oxidized metal impurity as a solid separate from the calcium.

2. In the method of purifying calcium contaminated with a metal impurity of lower boiling point, the improvement which comprises heating the calcium in the absence of air to a temperature at which the metal impurity of lower boiling point but not the calcium is distilled, selectively oxidizing the resulting metal impurity vapor in a zone removed from the main body of calcium, and collecting the oxidized metal impurity as a solid separate from the calcium.

3. In the method of purifying calcium contaminated with a metal impurity of lower boiling point, the improvement which comprises heating the calcium while under vacuum to a temperature at which the metal impurity of lower boiling point but not the calcium is distilled, selectively oxidizing the resulting metal impurity vapor in a. zone removed from the main body of calcium, and collecting the oxidized metal impurity as a solid separate from the calcium. 4. In the method of purifying calcium lcontaminated with a metal impurity of lower boiling point, the 'improvement which comprises heating the 'calcium to a temperature at which the metal impurity of lower boiling point -but not the calcium is distilled, selectively oxidizing q a solid separate from the calcium.

the resulting metal impurity vapor by bringing it in reactive contact with a refractory oxide in a zone removed fromthe main body of calcium, and collecting the oxidized metal impurity as 5. In the method of purifying calcium contaminated with a metal impurity of' lower boiling point, the improvement which comprises heating the calcium in the absencey of air to a temperature at ,which the metal impurity of lower boiling point but not the calcium is distilled, selectively oxidizing the resulting metal impurity by bringing it in reactive contact with titanium oxide in a zone removed from the main body of calcium, and collecting the oxidized metal vimpurity as a solid separate from the calcium.-

6. In the method of purifying calcium contaminated with a metal impurity of lower boiling point, the improvement which comprises heating the calcium in the absence of air to a temperature at which the metal impurity of lower boiling point but not the calcium is distilled, selectively oxidizing the resulting metal impurity vapor in a zone removed from the main body of calcium, collecting the oxidized metal impurity as a solid separate from the calcium, distilling the calcium, and condensing the resultin'g calcium vapor as a solid separate from the ,oxidized metal impurity in a zone intermediate that in which the metal impurity is oxidized and that from which the" main body of calcium is distilled.

7. In the -method of purifying calcium contory oxide in a zone removed from lthe main body of calcium, and collecting the oxidized sodium as a solid separate from the calcium.

8. In the method of purifying calcium contaminated with sodium as animpurity, the improvement whichcomprises heating the calcium in the absence of air to a temperature sufficiently high to-distill the sodium but not the calcium, selectively oxidizing the resulting sodium vapor by bringing it in reactive contact with titanium oxide in a zone removed from the main body of calcium, and collecting the oxidized sodium as a solid separate from the calcium.

9. Irl the method of purifying calcium contaminated with sodium as an impurity, the improvement which comprises heating the calcium in the absence of air to a temperature suiiiciently high to distill the sodium but not the calcium, selectively oxidizing the resulting sodium vapor by bringing it in reactive contact with a refractory oxide in a zone removed from the main body of calcium, distilling the calcium, and condensing the resulting calcium vapor as a solid separate from the oxidized sodium in a. zone intermediate that in which the sodium is oxiv dized and that from which the main body of calcium is distilled.

10. In the method of purifying calcium contaminated with potassium as an impurity, the improvement which comprise's'heating the calcium in the absence of air to aV temperature suflciently high to distill the potassium but not the calcium, selectively' oxidizing the resulting potassium vapor by bringing it in reactive contact with a, refractory oxide in a zone removed .from the main body of calcium, and collecting the oxidized potassium as a solid separate from the calcium.

11. In the method of purifying calcium contaminated with potassium as an impurity, the

.improvement which comprises heating thecalcium in the absence of air to a temperature sufciently high to distill the potassium but not the calcium, selectively oxidizing the resulting 'po- ,tassium vapor by bringingit in reactive contact with titanium oxide in a zone removed from the main body of calcium, and collecting the oxidized potassium as a solid separate from the calcium.

12. In the method of purifying. calcium contaminated with potassium as an impurity, the improvement which comprises heating the calcium in the absence of air to a temperature sufficiently high to distill the potassium but not the calcium,` selectively oxidizing the resulting potassium vapor by bringing it in reactive contact with a refractory oxide in a zone removed from the main body of calcium, distilling the calcium,

andI condensing the resulting calcium vapor as a solid separate from the oxidized potassium in a zone intermediate that inwhich the potassium is oxidized and that from whichthe main body of calcium is distilled.

13. In the method of purifying calcium contaminated with sodium and potassium as impurities, the improvement which comprises heating the calcium in the absence of air to a temperature suiiiciently high to distill the sodium and potassium but not the calcium, selectively oxidizing the resulting sodium and potassium vapors by bringing them in reactive contact witha 'refractory oxide in 'a zone removed'from the main body of calcium, and collecting the oxidized sodium and potassium as solids separate from the calcium.

14. In the method of purifying calcium contaminated with sodium and potassium as impurities, the improvement which comprisesheating the calcium in the absence of-air to a temperature suiciently high to distill the sodium and potassium but not the calcium, selectively oxidizing the resulting sodium andl potassium vapors by bringing them in reactive contact with titanium oxide ina zone removed from the` main body of calcium, and collecting the oxidized sodium and potassium as solids separate from the calcium.

15 In the method' of purifying calcium contaminated with sodium and potassium as impurities, the improvement which comprises heating the calcium in the absence of air to a temperature sumcientlyv high to distill the'sodium and potassium but not the calcium, selectively oxidizing the resulting sodium andl potassium vapors by bringing them in reactive contactwith a refractoryoxide in a zone removed from the main body of calcium, distilling the calcium, and condensing the resulting calcium vapor as a solid separate 40 from theoxidized sodium and potassium in a zone intermediate that in which the sodium and potassium are oxidized and that fromwhichthe main body of calcium is distilled.

16. In the method of purifying calcium conf taminated with sodium as an impurity, the improvement which comprises heating the calcium in the absence of air to a temperature sufficiently Ahigh to distill the sodium but not the calcium,

from the oxidized sodium in a. zone intermediate' that in which the sodium is oxidized and that from at which the metal impurity of lower boiling point but not the calcium is distilled, selectively oxidizing the resulting metal impurity by bringing it in reactive contactwith zirconium oxide in a zone removed from the main body of calcium, and col# lecting the oxidized metal impurity as separate from the calcium.

18. In the method of purifying calcium conz taminated with sodium as an impurity, the improvement which comprises heating the1 calcium a solid calcium, and collecting the oxidized sodium as a solid separate from the calcium.

19. In the method of purifying calcium contaminated with sodium as an impurity, the improvement which comprises heating the calcium in the absence of air to a temperature sumciently high to distill the sodium but not the calcium, selectively oxidizing the resulting sodium vapor by bringing it in reactive contact with zirconium oxide in a zone removed from the main body of calcium, distilling the calcium, and condensing the resulting calcium vapor as a solid separate from the oxidized sodium in a zone intermediate that in which the sodium is oxidized and that from which the main body of calcium is distilled.

20. In the method of purifying calcium contaminated with a metal impurity of lower boiling point, the improvement which comprises heating the calcium in the absence of air to a temperature at which the metal impurity of lower boiling point but not the calcium is distilled, selectively oxidizing the resulting metal impurity by bringing it in reactive contact with chromium oxide ina zone removed from the main body of calcium, and collecting the oxidized metal impurity as a solid separate from the calcium.

21. In the method of purifying calcium contaminated with sodium as an impurity, the improvement which comprises heating the calcium in the absence of air to a temperature suiiciently high to distill the sodium but not the calcium, selectively oxidizing the resulting sodium vapor by bringing it in reactive contact with chromium oxide in a zone removed from the main body of calcium,and collecting the oxidized sodium as a solid separate from the calcium.

22. In the method of purifying calcium cntaminated with sodium as an impurity, the improvement which comprises heating the calcium in the absence of air to a temperature sufficiently high to distill the sodium but not the calcium, selectively oxidizing the resulting sodium vapor by bringing it in reactive contact with chromium oxide in a zone removed from the main body of calcium, distilling the calcium, and condensing the resulting calcium vapor as a solid separate from the oxidized sodium in a zone intermediate that in which the sodium is oxidized and -that from which the main body of calcium is distilled.

PETER P. ALEXANDER. 

